The long-term goal of this research is to investigate the mechanism in human B-\and T-cell activation. Studies employing human peripheral blood, tonsil, and splenic lymphocytes indicate that Fc fragments derived from papain digestion, p'Fc fragments derived from plasmin digestion, aggregated immunoglobulin, and immune complexes are potent polyclonal activators. Studies designed to ascertain the cell-cell interaction requirements have revealed that both monocytes and T cells are required for the generation of polyclonal antibody. Fc fragments derived from a human IgG1 myeloma protein are capable of augmenting the in vitro anti-SRBC response of human PBL. The addition of Fc to cultures of human PBL along with SRBC resulted in a pronounced enhancement of the primary in vitro anti-SRBC response. Augmentation of the immune response is mediated by Fc and not the result of an artifact due to the addition of extraneous protein to culture because neither intact IgG1 nor Fab fragments possess any adjuvantproperties. (CS)